Method for in-line testing of flip-chip semiconductor assemblies

ABSTRACT

Flip-chip semiconductor assemblies, each including integrated circuit (IC) dice and an associated substrate, are electrically tested before encapsulation using an in-line or in-situ test socket or probes at a die-attach station. Those assemblies using “wet” quick-cure epoxies for die-attachment may be tested prior to the epoxy being cured by pressing the integrated circuit (IC) dice against interconnection points on the substrate for electrical connection, while those assemblies using “dry” epoxies may be cured prior to testing. In either case, any failures in the dice or in the interconnections between the dice and the substrates can be easily fixed, and the need for the use of known-good-die (KGD) rework procedures during repair is eliminated.

CROSS-REFERENCE TO THE RELATED APPLICATION

[0001] This application is a divisional of application Ser. No.09/166,369, filed Oct. 5, 1998, pending.

TECHNICAL FIELD

[0002] This invention relates in general to semiconductor manufacturingand, more specifically, to in-line testing of flip-chip semiconductorassemblies.

BACKGROUND OF THE INVENTION

[0003] As shown in FIG. 1, in a conventional process 10 formanufacturing flip-chip semiconductor assemblies, singulated dice areflip-chip attached with a conductive epoxy or solder to a printedcircuit board (PCB) or other substrate to form a flip-chip semiconductorassembly. Once the dice are attached by curing of the epoxy or reflow ofthe solder, the dice are then encapsulated, underfilled, or both, usinga non-conductive epoxy or other encapsulation material. The electricalcharacteristics of the flip-chip semiconductor assembly are then testedand, if the assembly passes the test, it is selected for shipping tocustomers.

[0004] If the flip-chip semiconductor assembly does not pass the test,then it proceeds to a repair station, where it is repaired using one ormore known-good dice (KGD) 12 (i.e., dice that have already passed allstandard electrical tests and have been through burn-in). Specifically,those dice in the assembly that are believed to have caused the assemblyto fail the test are electrically disconnected from the rest of theassembly, typically using laser fuses. One or more KGD are then attachedto the PCB of the assembly to replace the disconnected dice. Once theKGD are attached, the assembly is retested and, if it passes, it too isselected for shipping to customers.

[0005] The conventional KGD repair process described above generallyworks well to repair flip-chip semiconductor assemblies, but the processnecessary to produce KGD can be an expensive one. Also, the describedKGD repair process does not test for, or repair, problems with theinterconnections between the dice and the PCB in a flip-chipsemiconductor assembly. Rather, it only repairs problems withnon-functioning dice or defective solder bumps. Finally, the KGD in thedescribed repair process end up going through burn-in twice: a firsttime so they can be categorized as a KGD, and a second time when theflip-chip semiconductor assembly to which they are attached goes throughburn-in. This is obviously a waste of burn-in resources and alsostresses the KGD far beyond that necessary to weed out infantmortalities.

[0006] Therefore, there is a need in the art for a method of testingflip-chip semiconductor assemblies that reduces or eliminates the needfor the KGD repair process described above.

SUMMARY OF THE INVENTION

[0007] In a method for electrically testing a flip-chip semiconductorassembly in accordance with this invention, the assembly is testedusing, for example, an in-line or in-situ test socket or probes, afterone or more integrated circuit (IC) dice and a substrate, such as aprinted circuit board (PCB), are brought together to form the assembly,and before the IC dice are encapsulated or otherwise sealed forpermanent operation. As a result, any problems with the IC dice or theirinterconnection to the substrate can be fixed before sealing of the dicecomplicates repairs. The method thus avoids the problems associated withconventional known-good-die (KGD) repairs. Also, speed grading can beperformed while the dice are tested.

[0008] The assembly may be manufactured using a “wet” conductive epoxy,such as a heat-snap-curable, moisture curable, or radiation curableepoxy, in which case bond pads on the IC dice can be brought intocontact with conductive bumps on the substrate formed of the epoxy forthe testing, which can then be followed by curing of the epoxy to formpermanent die-to-substrate interconnects if the assembly passes thetest. If the assembly does not pass the test, the lack of curing allowsfor easy repair. After curing but before sealing of the IC dice, theassembly can be tested again to detect any interconnection problemsbetween the IC dice and the substrate.

[0009] The assembly may also be manufactured using a “dry” conductiveepoxy, such as a thermoplastic epoxy, for conductive die-attach, inwhich case the IC dice and the substrate can be brought together and theepoxy cured to form permanent die-to-substrate interconnections, afterwhich the testing may take place. Since the testing occurs beforesealing of the IC dice, repair is still relatively easy.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0010]FIG. 1 is a flow chart illustrating a conventional repair methodfor flip-chip semiconductor assemblies using known-good dice (KGD);

[0011]FIG. 2 is a flow chart illustrating a method for in-line testingof flip-chip semiconductor assemblies in accordance with this invention;

[0012]FIG. 3 is an isometric view of a flip-chip semiconductor assemblyand in-line test socket or probes implementing the method of FIG. 2;

[0013]FIG. 4 is a flow chart illustrating a method for in situ testingof flip-chip semiconductor assemblies in accordance with this invention;and

[0014]FIG. 5 is an isometric view of a flip-chip semiconductor assemblyand in situ test socket implementing the method of FIG. 4.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

[0015] As shown in FIGS. 2 and 3, in a process 20 for manufacturingflip-chip semiconductor assemblies in accordance with this invention, aprinted circuit board (PCB) 22 is indexed into a die attach station (notshown), where it is inserted into an in-line test socket 24 or contactedby probes 25. It will be understood by those having skill in thetechnical field of this invention that the invention is applicable notonly to PCBs, but also to a wide variety of other substrates used in themanufacture of flip-chip semiconductor assemblies.

[0016] When conductive epoxy dots 26 or “pads” deposited on the PCB 22at the die ends of die-to-board-edge conductive traces 30 are made froma “wet” epoxy (i.e., a quick-cure epoxy such as a heat-snap-curable,radiation-curable, or moisture-curable epoxy), then integrated circuit(IC) dice 28 are pressed (active surfaces down) against the dots 26during flip-chip attach so electrical connections are formed between thedice 28 and the in-line test socket 24 or probes 25 through the dots 26and conductive traces 30 on the PCB 22. Of course, it will be understoodthat the invention is also applicable to other flip-chip die-attachmethods including, for example, solder-based methods. It will also beunderstood that the dice 28 may be of any type, including, for example,Dynamic Random Access Memory (DRAM) dice, Static RAM (SRAM) dice,Synchronous DRAM (SDRAM) dice, microprocessor dice, Application-SpecificIntegrated Circuit (ASIC) dice, and Digital Signal Processor (DSP) dice.

[0017] Once such electrical connections are formed, an electrical testis performed on the flip-chip semiconductor assembly 32 formed by thedice 28 and the PCB 22 using the test socket 24 or probes 25. This testtypically involves checking for open connections that should be closed,and vice versa, but it can also involve more, fewer, or differentelectrical tests as need dictates. For example, the testing may alsoinclude speed grading the dice 28 for subsequent speed sorting. Also,the testing typically occurs while the PCB 22 is singulated from itscarrier (not shown).

[0018] If the assembly 32 fails the test, it is diverted to a reworkstation, where any dice 28 identified as being internally defective oras having a defective interconnection with the PCB 22 can easily beremoved and reworked, either by repairing the failing dice 28themselves, or by repairing conductive bumps (not shown) on the bottomsurfaces of the dice 28 used to connect the dice 28 to the conductiveepoxy dots 26 on the PCB 22. Once repaired, the assembly 32 returns forretesting and, if it passes, it is advanced in the process 20 for quickcuring along with all assemblies 32 that passed the test the first timethrough.

[0019] During quick cure, the “wet” epoxy dots 26 of the assembly 32 arecured, typically using heat, radiation, or moisture. The assembly 32 isthen electrically tested again to ensure that the quick curing has notdisrupted the interconnections between the dice 28 and the conductivetraces 30 through the conductive epoxy dots 26 and the bumps (not shown)on the bottom surfaces of the dice 28. If quick curing has disruptedthese interconnections, then the assembly 32 proceeds to the reworkstation, where the connections between the bumps and the dots 26 can berepaired. The repaired assembly 32 is then retested and, if it passes,it proceeds to encapsulation (or some other form of sealing) and,ultimately, is shipped to customers along with those assemblies 32 thatpassed this testing step the first time through. Of course, it should beunderstood that this invention may be implemented with only one teststage for “wet” epoxy assemblies, although two stages are preferable.

[0020] When the conductive epoxy dots 26 are made from a “dry” epoxy(e.g., a thermoplastic epoxy), then the PCB 22 is indexed and insertedinto the test socket 24 or connected to the probes 25 as describedabove, but the dice 28 are attached to the PCB 22 using heat before theassembly 32 proceeds to testing. Testing typically takes place while thePCB 22 is singulated from its carrier (not shown).

[0021] During testing, if the assembly 32 fails, then it proceeds to arework station, where the bumps on the bottom of the dice 28, the dice28 themselves, or the interconnection between the bumps and theconductive epoxy dots 26 can be repaired. The repaired assembly 32 thenproceeds to encapsulation (or some other form of sealing) and,eventually, is shipped to customers along with those assemblies 32 thatpassed the testing the first time through.

[0022] Thus, this invention provides a repair method for flip-chipsemiconductor assemblies that is less expensive than the previouslydescribed known-good-die (KGD) based rework process, because it does notrequire the pretesting of dice that the KGD process requires. Also, themethods of this invention are applicable to testing for both internaldie defects and die-to-PCB interconnection defects, and to repairinginterconnections between dice and a PCB in a flip-chip semiconductorassembly, whereas the conventional KGD process is not. In addition,these inventive methods do not waste burn-in resources, in contrast tothe conventional KGD process previously described. Finally, thisinvention allows for early and convenient speed grading of flip-chipsemiconductor assemblies.

[0023] As shown in FIGS. 4 and 5, in a process 40 for manufacturingflip-chip semiconductor assemblies in accordance with this invention, aprinted circuit board (PCB) 42 is indexed into a die attach station (notshown), where it is inserted into an in situ test socket 44. It will beunderstood by those having skill in the technical field of thisinvention that the invention is applicable not only to PCBs, but also toa wide variety of other substrates used in the manufacture of flip-chipsemiconductor assemblies.

[0024] When conductive epoxy dots 46 or “pads” deposited on the PCB 42at the die ends of die-to-board-edge conductive traces 50 are made froma “wet” epoxy (i.e., a quick-cure epoxy such as a heat-snap-curable,radiation-curable, or moisture-curable epoxy), then integrated circuit(IC) dice 48 are pressed (active surfaces down) against the dots 46during flip-chip attach so electrical connections are formed between thedice 48 and the in situ test socket 44 through the dots 46 andconductive traces 50 on the PCB 42. Of course, it will be understoodthat the invention is also applicable to other flip-chip die-attachmethods including, for example, solder-based methods. It will also beunderstood that the dice 48 may be of any type, including, for example,Dynamic Random Access Memory (DRAM) dice, Static RAM (SRAM) dice,Synchronous DRAM (SDRAM) dice, microprocessor dice, Application-SpecificIntegrated Circuit (ASIC) dice, and Digital Signal Processor (DSP) dice.

[0025] Once such electrical connections are formed, an electrical testis performed on the flip-chip semiconductor assembly 52 formed by thedice 48 and the PCB 42 using the test socket 44. This test typicallyinvolves checking for open connections that should be closed, and viceversa, but it can also involve more, fewer, or different electricaltests as need dictates. If the assembly 52 fails the test, it isdiverted to a rework station, where any dice 48 identified as beinginternally defective or as having a defective interconnection with thePCB 42 can easily be removed and reworked, either by repairing thefailing dice 48 themselves, or by repairing conductive bumps (not shown)on the bottom surfaces of the dice 48 used to connect the dice 48 to theconductive epoxy dots 46 on the PCB 42. Once repaired, the assembly 52returns for retesting and, if it passes, it is advanced in the process40 for quick curing along with all assemblies 52 that passed the testthe first time through.

[0026] During quick cure, the “wet” epoxy dots 46 of the assembly 52 arecured, typically using heat, radiation, or moisture. The assembly 52 isthen electrically tested again to ensure that the quick curing has notdisrupted the interconnections between the dice 48 and the conductivetraces 50 through the conductive epoxy dots 46 and the bumps (not shown)on the bottom surfaces of the dice 48. If quick curing has disruptedthese interconnections, then the assembly 52 proceeds to another reworkstation, where the connections between the bumps and the dots 46 can berepaired. The repaired assembly 52 is then retested and, if it passes,it proceeds to encapsulation (or some other form of sealing) and,ultimately, is shipped to customers along with those assemblies 52 thatpassed this testing step the first time through. Of course, it should beunderstood that this invention may be implemented with only one teststage for “wet” epoxy assemblies, although the two stages shown in FIG.4 are preferable.

[0027] When the conductive epoxy dots 46 are made from a “dry” epoxy(e.g., a thermoplastic epoxy), then the PCB 42 is indexed and insertedinto the test socket 44 as described above, but the dice 48 are attachedto the PCB 42 using heat before the assembly 52 proceeds to testing.During testing, if the assembly 52 fails, then it proceeds to a reworkstation, where the bumps on the bottom of the dice 48, the dice 48themselves, or the interconnection between the bumps and the conductiveepoxy dots 46 can be repaired. The repaired assembly 52 then proceeds toencapsulation (or some other form of sealing) and, eventually, isshipped to customers along with those assemblies 52 that passed thetesting the first time through.

[0028] Thus, this invention provides a repair method for flip-chipsemiconductor assemblies that is less expensive than the previouslydescribed known-good-die (KGD) based rework process, because it does notrequire the pretesting of dice that the KGD process requires. Also, themethods of this invention are applicable to testing for both internaldie defects and die-to-PCB interconnection defects, and to repairinginterconnections between dice and a PCB in a flip-chip semiconductorassembly, whereas the conventional KGD process is not. In addition,these inventive methods do not waste burn-in resources, in contrast tothe conventional KGD process previously described.

[0029] Although this invention has been described with reference toparticular embodiments, the invention is not limited to these describedembodiments. Rather, the invention is limited only by the appendedclaims, which include within their scope all equivalent methods thatoperate according to the principles of the invention as described.

We claim:
 1. A method for electrically testing a flip-chip semiconductorassembly during its manufacture, the assembly being formed from asubstrate and one or more integrated circuit (IC) dice, the methodcomprising: connecting the substrate to a test apparatus at a die-attachstation; singulating the substrate from a carrier; bringing the IC diceinto a flip-chip-type conductive contact with the substrate while it isconnected to the test apparatus at the die-attach station to form theflip-chip semiconductor assembly; and electrically testing the assemblyat the die-attach station using the test apparatus.
 2. The method ofclaim 1 wherein the act of connecting the substrate to the testapparatus includes at least one of inserting the substrate into anin-line test socket and contacting the substrate with probes.
 3. Themethod of claim 1 wherein the act of bringing the IC dice into aflip-chip-type conductive contact with the substrate comprises pressingthe IC dice against a surface of the substrate so interconnection bumpson the dice are in conductive contact with conductive pads on thesurface of the substrate.
 4. The method of claim 1 wherein the act ofbringing the IC dice into a flip-chip-type conductive contact with thesubstrate comprises flip-chip-attaching the IC dice to the substrate. 5.A method for electrically testing a flip-chip semiconductor assemblyformed from at least one integrated circuit (IC) die and a substrate,the method comprising: contacting the substrate with probes; while thesubstrate is in contact with the probes, bringing the at least one dieand the substrate together in conductive contact to form the flip-chipsemiconductor assembly; and before the at least one die is sealed,electrically testing the assembly using the probes.
 6. The method ofclaim 5 wherein the act of contacting the substrate with the probescomprises contacting the substrate with the probes at a die-attachstation.
 7. A method for in situ electrical testing of a flip-chipsemiconductor assembly during its manufacture, the method comprising:providing one or more integrated circuit (IC) dice, each with a surfacehaving interconnection bumps thereon; providing a substrate withconductive pads deposited on a surface thereof for flip-chip attachmentto the interconnection bumps of the IC dice; providing a plurality ofprobes for contacting the substrate; contacting the substrate with theprobes; positioning the IC dice on the surface of the substrate with theinterconnection bumps of the dice in conductive contact with the pads ofthe substrate to form the flip-chip semiconductor assembly; while thesubstrate is in contact with the probes and the IC dice are positionedon the surface of the substrate, and before sealing of the IC dice,electrically testing the assembly using the probes; repairing theassembly if it fails the electrical testing; and sealing the IC dice ofthe assembly.
 8. The method of claim 7 wherein the act of providing oneor more IC dice comprises providing one or more IC dice selected from agroup comprising Dynamic Random Access Memory (DRAM) IC dice, Static RAM(SRAM) IC dice, Synchronous DRAM (SDRAM) IC dice, microprocessor ICdice, Application-Specific IC (ASIC) dice, and Digital Signal Processor(DSP) dice.
 9. The method of claim 7 wherein the act of providing one ormore IC dice, each with a surface having interconnection bumps thereon,comprises providing one or more IC dice, each with a surface havinginterconnection bumps made from solder thereon.
 10. The method of claim7 wherein the act of providing a substrate comprises providing a printedcircuit board (PCB).
 11. The method of claim 7 wherein the act ofproviding a substrate with conductive pads deposited on a surfacethereof comprises providing a substrate with conductive pads made from amaterial selected from a group comprising conductive epoxy and solder.12. The method of claim 11 wherein the act of providing a substratecomprises providing a substrate with conductive pads made from amaterial selected from a group comprising thermoplastic epoxy andquick-curable epoxy.
 13. The method of claim 7 wherein the act ofrepairing the assembly includes at least one of: removing and replacingat least one of the IC dice of the assembly; repairing theinterconnection bumps of the at least one of the IC dice of theassembly; and repairing at least some of the conductive pads of thesubstrate.
 14. The method of claim 7 wherein the act of sealing the ICdice of the assembly comprises at least one of encapsulating the IC diceof the assembly and underfilling the IC dice of the assembly.
 15. Amethod for in-line electrical testing of a flip-chip semiconductorassembly during its manufacture, the method comprising: providing one ormore integrated circuit (IC) dice, each with a surface havinginterconnection bumps thereon; providing a printed circuit board (PCB)with conductive epoxy pads deposited on a surface thereof for flip-chipattachment to the interconnection bumps of the IC dice; providing anin-line electrical test socket for connection to the PCB; inserting thePCB into the test socket; positioning the IC dice on the surface of thePCB with the interconnection bumps of the dice in conductive contactwith the epoxy pads of the PCB to form the flip-chip semiconductorassembly; attaching the IC dice to the PCB; while the PCB is inserted inthe test socket and before encapsulation of the IC dice, electricallytesting the assembly using the test socket; repairing the assembly if itfails the electrical testing; and encapsulating the IC dice of theassembly.
 16. A method for in-line electrical testing of a flip-chipsemiconductor assembly during its manufacture, the method comprising:providing one or more integrated circuit (IC) dice, each with a surfacehaving interconnection bumps thereon; providing a substrate withconductive quick-cure epoxy pads deposited on a surface thereof forflip-chip attachment to the interconnection bumps of the IC dice;providing an in-line electrical test socket for connection to thesubstrate; inserting the substrate into the test socket; positioning theIC dice on the surface of the substrate and pressing the interconnectionbumps of the dice into conductive contact with the epoxy pads of thesubstrate to form the flip-chip semiconductor assembly; attaching the ICdice to the substrate; while the substrate is inserted into the testsocket and before sealing of the IC dice, electrically testing theassembly using the test socket; repairing the assembly if it fails theelectrical testing; curing the quick-cure conductive epoxy pads of thesubstrate; and sealing the IC dice of the assembly.
 17. A method forelectrically testing a flip-chip semiconductor assembly formed from atleast one integrated circuit (IC) die and a substrate, the methodcomprising electrically testing the assembly after the at least one dieand the substrate are brought together to form the assembly and beforethe at least one die is sealed.
 18. A method for electrically testing aflip-chip semiconductor assembly during its manufacture, the assemblybeing formed from a substrate and one or more integrated circuit (IC)dice, the method comprising: connecting the substrate to a testapparatus at a die-attach station; bringing the IC dice into aflip-chip-type conductive contact with the substrate while it isconnected to the test apparatus at the die-attach station to form theflip-chip semiconductor assembly; and electrically testing the assemblyat the die-attach station using the test apparatus.
 19. The method ofclaim 18 wherein the act of bringing the IC dice into a flip-chip-typeconductive contact with the substrate comprises pressing the IC diceagainst a surface of the substrate so interconnection bumps on the diceare in conductive contact with conductive pads on the surface of thesubstrate.
 20. The method of claim 18 wherein the act of bringing the ICdice into a flip-chip-type conductive contact with the substratecomprises flip-chip-attaching the IC dice to the substrate.
 21. A methodfor electrically testing a flip-chip semiconductor assembly formed fromat least one integrated circuit (IC) die and a substrate, the methodcomprising: inserting the substrate into a test socket; while thesubstrate is in the test socket, bringing the at least one die and thesubstrate together in conductive contact to form the flip-chipsemiconductor assembly; and before the at least one die is sealed,electrically testing the assembly using the test socket.
 22. A methodfor in situ electrical testing of a flip-chip semiconductor assemblyduring its manufacture, the method comprising: providing one or moreintegrated circuit (IC) dice, each with a surface having interconnectionbumps thereon; providing a substrate with conductive pads deposited on asurface thereof for flip-chip attachment to the interconnection bumps ofthe IC dice; providing an in situ electrical test socket for connectionto the substrate; inserting the substrate into the test socket;positioning the IC dice on the surface of the substrate with theinterconnection bumps of the dice in conductive contact with the pads ofthe substrate to form the flip-chip semiconductor assembly; while thesubstrate is inserted into the test socket and the IC dice arepositioned on the surface of the substrate, and before sealing of the ICdice, electrically testing the assembly using the test socket; repairingthe assembly if it fails the electrical testing; and sealing the IC diceof the assembly.
 23. A method for in situ electrical testing of aflip-chip semiconductor assembly during its manufacture, the methodcomprising: providing one or more integrated circuit (IC) dice, eachwith a surface having interconnection bumps thereon; providing a printedcircuit board (PCB) with conductive epoxy pads deposited on a surfacethereof for flip-chip attachment to the interconnection bumps of the ICdice; providing an in situ electrical test socket for connection to thePCB; inserting the PCB into the test socket; positioning the IC dice onthe surface of the PCB with the interconnection bumps of the dice inconductive contact with the epoxy pads of the PCB to form the flip-chipsemiconductor assembly; while the PCB is inserted in the test socket andthe IC dice are positioned on the surface of the PCB, and beforeencapsulation of the IC dice, electrically testing the assembly usingthe test socket; repairing the assembly if it fails the electricaltesting; and encapsulating the IC dice of the assembly.
 24. A method forin situ electrical testing of a flip-chip semiconductor assembly duringits manufacture, the method comprising: providing one or more integratedcircuit (IC) dice, each with a surface having interconnection bumpsthereon; providing a substrate with conductive quick-cure epoxy padsdeposited on a surface thereof for flip-chip attachment to theinterconnection bumps of the IC dice; providing an in situ electricaltest socket for connection to the substrate; inserting the substrateinto the test socket; positioning the IC dice on the surface of thesubstrate and pressing the interconnection bumps of the dice intoconductive contact with the epoxy pads of the substrate to form theflip-chip semiconductor assembly; while the substrate is inserted intothe test socket and the IC dice are positioned on the surface of thesubstrate, and before sealing of the IC dice, electrically testing theassembly using the test socket; repairing the assembly if it fails theelectrical testing; curing the quick-cure conductive epoxy pads of thesubstrate; and sealing the IC dice of the assembly.
 25. A method for insitu electrical testing of a flip-chip semiconductor assembly during itsmanufacture, the method comprising: providing one or more integratedcircuit (IC) dice, each with a surface having interconnection bumpsthereon; providing a substrate with conductive epoxy pads deposited on asurface thereof for flip-chip attachment to the interconnection bumps ofthe IC dice; providing an in situ electrical test socket for connectionto the substrate; inserting the substrate into the test socket;positioning the IC dice on the surface of the substrate with theinterconnection bumps of the dice in conductive contact with the epoxypads of the substrate to form the flip-chip semiconductor assembly;curing the conductive epoxy pads of the substrate; while the substrateis inserted into the test socket and the IC dice are positioned on thesurface of the substrate, and before sealing of the IC dice,electrically testing the assembly using the test socket; repairing theassembly if it fails the electrical testing; and sealing the IC dice ofthe assembly.